The 3.92 gear doesn't KILL fuel mileage.Thats been discussed many times before.In fact in certain conditions it gets BETTER fuel mileage.Takes less H.P. to move the truck then it does with a tall 3.21 gear.

 

3.21 compared to 3.92 will not make much of a difference, but 3.21 to 4.10 gears would make a significant difference,
FF

 

whats the 09 sound like with the cutout you have a video ?

 

This might be a question with an obvious answer, but somebody said in this thread that 17's and 20" rim make a difference in acceleration. How does that make a difference. overall circumference of the tire is the same. maybe slight weight difference since there is less rubber or what?

 

I have an 09 Laramie with the 3.92 and 14" Magnaflow and mine has plenty of power. I have raced a few other 4th gens off the line and have not lost yet. I could really tell who had the 3.21 and 3.55 so I would have to say that yes it is the gearing that makes the difference. I also have the 20" wheels.

 

The 17's effectively lower your gear ratio compared to 20's and you get out of the hole better. Also, the 20's weigh more thus more rotating mass to egt going. I dont think the tire height to ground is the same for 17's and 20's though.

 

275/60/20 tire = 33" Diameter
265/70/17 tire = 31.6" Diameter

About a 4% difference in rear wheel torque

 

Glad mine has 3.92s